Cryopump

ABSTRACT

A cryopump includes a cryopump housing and a water absorbing layer mounted on an outer side of the cryopump housing.

RELATED APPLICATIONS

The contents of Japanese Patent Application No. 2018-028677, and ofInternational Patent Application No. PCT/JP2019/006063, on the basis ofeach of which priority benefits are claimed in an accompanyingapplication data sheet, are in their entirety incorporated herein byreference.

BACKGROUND Technical Field

Certain embodiments of the present invention relate to a cryopump.

Description of Related Art

A cryopump is a vacuum pump which captures gas molecules on a cryopanelcooled to a cryogenic temperature by condensation or adsorption toexhaust the gas molecules. The cryopump is generally used to realize aclean vacuum environment which is required for a semiconductor circuitmanufacturing process or the like. Since the cryopump is a so-called gasaccumulation type vacuum pump, regeneration to periodically dischargethe captured gas to the outside is required.

SUMMARY

According to an embodiment of the present invention, there is provided acryopump including: a cryopump housing; and a water absorbing layermounted on an outer side of the cryopump housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view schematically showing a cryopumpaccording to an embodiment and a dew condensation suppressing structurethereof.

FIG. 2 is a sectional view taken along line II-II, schematically showingthe cryopump shown in FIG. 1.

FIG. 3 is a schematic diagram showing another example of the dewcondensation suppressing structure according to the embodiment.

FIG. 4 is a schematic diagram showing another example of the dewcondensation suppressing structure according to the embodiment.

FIG. 5 is a schematic diagram showing another example of the dewcondensation suppressing structure according to the embodiment.

DETAILED DESCRIPTION

If the regeneration of the cryopump is started, the vacuum in a cryopumphousing that accommodates a cryopanel is released. The interior of thehousing is filled with gas due to-re-vaporization of an accumulated gasor introduction of a purge gas. At the beginning of the regeneration,the cryopanel is still cooled to a cryogenic temperature. Since a vacuumadiabatic effect is lost due to the gas filling, the housing can becooled through the gas by the cryopanel. Since the housing is exposed tothe ambient environment, in some cases, dew condensation may occur onthe outer surface thereof. Condensed water may drop.

It is desirable to suppress dew condensation on a cryopump or tosuppress dropping of condensed water.

Any combination of the constituent elements described above, orreplacement of constituent elements or expressions of the presentinvention with each other between methods, apparatuses, systems, or thelike is also valid as an aspect of the present invention.

According to the present invention, it is possible to suppress dewcondensation on the cryopump or to suppress dropping of condensed water.

Hereinafter, modes for carrying out the present invention will bedescribed in detail with reference to the drawings. In the descriptionand the drawings, identical or equivalent constituent elements, members,and processing are denoted by the same reference numerals, andoverlapping description is omitted appropriately. The scales or shapesof the respective parts shown in the drawings are set for convenience inorder to facilitate description and are not interpreted to a limitedextent unless otherwise specified. Embodiments are exemplification anddo not limit the scope of the present invention. All features describedin the embodiments or combinations thereof are not necessarily essentialto the invention.

FIG. 1 is a side sectional view schematically showing a cryopump 10according to an embodiment. FIG. 2 is a sectional view taken along lineII-II, schematically showing the cryopump 10 shown in FIG. 1. FIG. 1shows a cross section including a cryopump central axis C indicated by adashed-dotted line. Further, for easy understanding, in FIG. 1, alow-temperature cryopanel part and a cryocooler of the cryopump 10 areshown not in a cross section but in a side view.

As will be described later, the cryopump 10 has a dew condensationsuppressing structure.

The cryopump 10 is mounted to a vacuum chamber of, for example, an ionimplanter, a sputtering apparatus, a vapor deposition apparatus, orother vacuum process equipment and is used to increase the degree ofvacuum in the interior of the vacuum chamber to a level which isrequired for a desired vacuum process. The cryopump 10 has an intakeport 12 for receiving a gas to be exhausted from the vacuum chamber. Thegas enters an internal space 14 of the cryopump 10 through the intakeport 12.

The cryopump 10 may be intended to be installed at and used in thevacuum chamber in the direction shown in the drawing, that is, in aposture in which the intake port 12 is directed upward. However, theposture of the cryopump 10 is not limited thereto, and the cryopump 10may be installed at the vacuum chamber in another direction.

In the following, there is a case where the terms “axial direction” and“radial direction” are used in order to express the positionalrelationship between constituent elements of the cryopump 10 in aneasily understandable manner. The axial direction represents a directionpassing through the intake port 12 (in FIG. 1, a direction along thecryopump central axis C passing through the center of the intake port12), and the radial direction represents a direction along the intakeport 12 (a direction perpendicular to the central axis C). Forconvenience, with respect to the axial direction, there is a case wherethe side relatively close to the intake port 12 is referred to as an“upper side” and the side relatively distant from the intake port 12 isreferred to as a “lower side”. That is, there is a case where the siderelatively distance from the bottom of the cryopump 10 is referred to asan “upper side” and the side relatively close to the bottom of thecryopump 10 is referred to as a “lower side”. With respect to the radialdirection, there is a case where the side close to the center of theintake port 12 (in FIG. 1, the central axis C) is referred to as an“inner side” and the side close to the peripheral edge of the intakeport 12 is referred to as an “outer side”. Such expressions are notrelated to the disposition when the cryopump 10 is mounted to the vacuumchamber. For example, the cryopump 10 may be mounted to the vacuumchamber with the intake port 12 facing downward in the verticaldirection.

Further, there is a case where a direction surrounding the axialdirection is referred to as a “circumferential direction”. Thecircumferential direction is a second direction along the intake port 12and is a tangential direction orthogonal to the radial direction.

The cryopump 10 includes a cryocooler 16, a first-stage cryopanel 18, asecond-stage cryopanel assembly 20, and a cryopump housing 70. Thefirst-stage cryopanel 18 may be referred to as a high-temperaturecryopanel part or a 100 K part. The second-stage cryopanel assembly 20may be referred to as a low-temperature cryopanel part or a 10 K part.

The cryocooler 16 is a cryocooler such as a Gifford McMahon typecryocooler (a so-called GM cryocooler), for example. The cryocooler 16is a two-stage cryocooler. Therefore, the cryocooler 16 includes a firstcooling stage 22 and a second cooling stage 24. The cryocooler 16 isconfigured to cool the first cooling stage 22 to a first coolingtemperature and cool the second cooling stage 24 to a second coolingtemperature. The second cooling temperature is lower than the firstcooling temperature. For example, the first cooling stage 22 is cooledto a temperature in a range of about 65 K to 120 K, preferably, in arange of 80 K to 100 K, and the second cooling stage 24 is cooled to atemperature in a range of about 10 K to 20 K.

Further, the cryocooler 16 includes a cryocooler structure part 21 thatstructurally supports the second cooling stage 24 on the first coolingstage 22 and structurally supports the first cooling stage 22 on a roomtemperature part 26 of the cryocooler 16. Therefore, the cryocoolerstructure part 21 includes a first cylinder 23 and a second cylinder 25that extend coaxially along the radial direction. The first cylinder 23connects the room temperature part 26 of the cryocooler 16 to the firstcooling stage 22. The second cylinder 25 connects the first coolingstage 22 to the second cooling stage 24. The room temperature part 26,the first cylinder 23, the first cooling stage 22, the second cylinder25, and the second cooling stage 24 are linearly arranged in this order.

A first displacer and a second displacer (not shown) are reciprocallydisposed in the interiors of the first cylinder 23 and the secondcylinder 25, respectively. A first regenerator and a second regenerator(not shown) are respectively incorporated into the first displacer andthe second displacer. Further, the room temperature part 26 has a drivemechanism (not shown) for reciprocating the first displacer and thesecond displacer. The drive mechanism includes a flow path switchingmechanism that switches a flow path of a working gas (for example,helium) so as to periodically repeat the supply and discharge of theworking gas to and from the interior of the cryocooler 16.

The first cooling stage 22 is installed at the first-stage lowtemperature end of the cryocooler 16. The first cooling stage 22 is amember that encloses an end portion of the first cylinder 23 on the sideopposite to the room temperature part 26 and surrounds a first expansionspace for the working gas. The first expansion space is a variablevolume that is formed between the first cylinder 23 and the firstdisplacer in the interior of the first cylinder 23 and that changes involume according to the reciprocation of the first displacer. The firstcooling stage 22 is formed of a metal material having a higher thermalconductivity than the first cylinder 23. For example, the first coolingstage 22 is formed of copper and the first cylinder 23 is formed ofstainless steel.

The second cooling stage 24 is installed at a second-stage lowtemperature end of the cryocooler 16. The second cooling stage 24 is amember that encloses an end portion of the second cylinder 25 on theside opposite to the room temperature part 26 and surrounds a secondexpansion space for the working gas. The second expansion space is avariable volume that is formed between the second cylinder 25 and thesecond displacer in the interior of the second cylinder 25 and thatchanged in volume according to the reciprocation of the seconddisplacer. The second cooling stage 24 is formed of a metal materialhaving a higher thermal conductivity than the second cylinder 25. Thesecond cooling stage 24 is formed of copper, and the second cylinder 25is formed of stainless steel. In FIG. 1, a boundary 24 b between thesecond cooling stage 24 and the second cylinder 25 is shown.

The cryocooler 16 is connected to a compressor (not shown) for theworking gas. The cryocooler 16 cools the first cooling stage 22 and thesecond cooling stage 24 by expanding the working gas pressurized by thecompressor in the interior thereof. The expanded working gas isrecovered to the compressor and pressurized again. The cryocooler 16generates cold by repeating a heat cycle including the supply anddischarge of the working gas and the reciprocation of the firstdisplacer and the second displacer in synchronization with the supplyand discharge of the working gas.

The cryopump 10 which is shown in the drawing is a so-called horizontalcryopump. The horizontal cryopump is generally a cryopump in which thecryocooler 16 is disposed so as to intersect (usually, be orthogonal to)the central axis C of the cryopump 10. The first cooling stage 22 andthe second cooling stage 24 of the cryocooler 16 are arranged in thedirection perpendicular to the cryopump central axis C (the horizontaldirection in FIG. 1, or the direction of a central axis D of thecryocooler 16).

The first-stage cryopanel 18 includes a radiation shield 30 and an inletcryopanel 32 and surrounds the second-stage cryopanel assembly 20. Thefirst-stage cryopanel 18 is a cryopanel provided in order to protect thesecond-stage cryopanel assembly 20 from radiant heat outside thecryopump 10 or from the cryopump housing 70. The first-stage cryopanel18 is thermally coupled to the first cooling stage 22. Accordingly, thefirst-stage cryopanel 18 is cooled to the first cooling temperature. Thefirst-stage cryopanel 18 has a gap between itself and the second-stagecryopanel assembly 20, and the first-stage cryopanel 18 is not incontact with the second-stage cryopanel assembly 20.

The radiation shield 30 is provided to protect the second-stagecryopanel assembly 20 from the radiant heat of the cryopump housing 70.The radiation shield 30 is located between the cryopump housing 70 andthe second-stage cryopanel assembly 20 and surrounds the second-stagecryopanel assembly 20. The radiation shield 30 has a shield main opening34 for receiving gas from the outside of the cryopump 10 into theinternal space 14. The shield main opening 34 is located at the intakeport 12.

The radiation shield 30 is provided with a shield front end 36 definingthe shield main opening 34, a shield bottom portion 38 which is locatedon the side opposite to the shield main opening 34, and a shield sideportion 40 connecting the shield front end 36 to the shield bottomportion 38. The shield front end 36 forms a part of the shield sideportion 40. The shield side portion 40 extends in the axial directionfrom the shield front end 36 to the side opposite to the shield mainopening 34, and extends so as to surround the second cooling stage 24 inthe circumferential direction. The radiation shield 30 has a tubular(for example, cylindrical) shape closed at the shield bottom portion 38,and is formed in a cup shape. An annular gap 42 is formed between theshield side portion 40 and the second-stage cryopanel assembly 20.

The shield bottom portion 38 may be a member separate from the shieldside portion 40. For example, the shield bottom portion 38 may be a flatdisk having substantially the same diameter as the shield side portion40, and may be attached to the shield side portion 40 on the sideopposite to the shield main opening 34. Further, at least a part of theshield bottom portion 38 may be open. For example, the radiation shield30 may not be closed by the shield bottom portion 38. That is, both endsof the shield side portion 40 may be open.

The shield side portion 40 has a shield side portion opening 44 intowhich the cryocooler structure part 21 is inserted. The second coolingstage 24 and the second cylinder 25 are inserted into the radiationshield 30 from outside the radiation shield 30 through the shield sideportion opening 44. The shield side portion opening 44 is a mountinghole formed in the shield side portion 40 and is, for example, circular.The first cooling stage 22 is disposed outside the radiation shield 30.

The shield side portion 40 is provided with a mounting seat 46 for thecryocooler 16. The mounting seat 46 is a flat portion for mounting thefirst cooling stage 22 to the radiation shield 30, and is slightlydepressed when viewed from outside the radiation shield 30. The mountingseat 46 forms the outer periphery of the shield side portion opening 44.The mounting seat 46 is closer to the shield bottom portion 38 than theshield front end 36 in the axial direction. The first cooling stage 22is mounted to the mounting seat 46, whereby the radiation shield 30 isthermally coupled to the first cooling stage 22.

The inlet cryopanel 32 is provided in the shield main opening 34 inorder to protect the second-stage cryopanel assembly 20 from the radiantheat from a heat source outside the cryopump 10. The heat source outsidethe cryopump 10 is, for example, a heat source in the vacuum chamber towhich the cryopump 10 is mounted. The inlet cryopanel 32 can restrictnot only the radiant heat but also the entry of gas molecules. The inletcryopanel 32 occupies a part of the opening area of the shield mainopening 34 so as to limit the gas flow into the internal space 14through the shield main opening 34 to a desired amount. An annular openarea 48 is formed between the inlet cryopanel 32 and the shield frontend 36.

The inlet cryopanel 32 is mounted to the shield front end 36 by anappropriate mounting member and is thermally coupled to the radiationshield 30. The inlet cryopanel 32 is thermally coupled to the firstcooling stage 22 through the radiation shield 30. The inlet cryopanel 32has, for example, a plurality of annular or linear vanes. Alternatively,the inlet cryopanel 32 may be a single plate-shaped member.

The second-stage cryopanel assembly 20 is mounted to the second coolingstage 24 so as to surround the second cooling stage 24. Accordingly, thesecond-stage cryopanel assembly 20 is thermally coupled to the secondcooling stage 24, and the second-stage cryopanel assembly 20 is cooledto the second cooling temperature. The second-stage cryopanel assembly20 is surrounded together with the second cooling stage 24 by the shieldside portion 40.

The second-stage cryopanel assembly 20 includes a top cryopanel 60facing the shield main opening 34, a plurality of (in this example, two)cryopanel members 62, and a cryopanel mounting member 64.

Further, as shown in FIG. 1, the cryopump 10 includes a cryopanelpositioning member 67. A heat transfer part that thermally couples thesecond-stage cryopanel assembly 20 to the second cooling stage 24includes the cryopanel mounting member 64 and the cryopanel positioningmember 67. The top cryopanel 60 and the cryopanel members 62 are mountedto the second cooling stage 24 through the cryopanel mounting member 64and the cryopanel positioning member 67.

Since the annular gap 42 is formed between the top cryopanel 60 and thecryopanel members 62, and the shield side portion 40, neither the topcryopanel 60 nor the cryopanel members 62 are in contact with theradiation shield 30. The cryopanel members 62 are covered by the topcryopanel 60.

The top cryopanel 60 is a portion of the second-stage cryopanel assembly20 closest to the inlet cryopanel 32. The top cryopanel 60 is disposedbetween the shield main opening 34 or the inlet cryopanel 32 and thecryocooler 16 in the axial direction. The top cryopanel 60 is located atthe central portion of the internal space 14 of the cryopump 10 in theaxial direction. Therefore, a main accommodation space 65 for acondensation layer is widely formed between the front surface of the topcryopanel 60 and the inlet cryopanel 32. The main accommodation space 65for the condensation layer occupies the upper half of the internal space14.

The top cryopanel 60 is a substantially flat cryopanel disposedperpendicular to the axial direction. That is, the top cryopanel 60extends in the radial direction and the circumferential direction. Asshown in FIG. 2, the top cryopanel 60 is a disk-shaped panel having adimension (for example, a projected area) larger than that of the inletcryopanel 32. However, the relationship between the dimensions of thetop cryopanel 60 and the inlet cryopanel 32 is not limited to this, andthe dimension of the top cryopanel 60 may be smaller than that of theinlet cryopanel 32, or the top cryopanel 60 and the inlet cryopanel 32may have substantially the same dimension.

The top cryopanel 60 is disposed so as to form a gap region 66 betweenitself and the cryocooler structure part 21. The gap region 66 is a voidformed in the axial direction between the back surface of the topcryopanel 60 and the second cylinder 25.

The cryopanel member 62 is provided with an adsorbent 74 such asactivated carbon. The adsorbent 74 is bonded to the back surface of thecryopanel member 62, for example. It is intended that the front surfaceof the cryopanel member 62 functions as a condensation surface and theback surface functions as an adsorption surface. The adsorbent 74 may beprovided on the front surface of the cryopanel member 62. Similarly, thetop cryopanel 60 may have the adsorbent 74 on the front surface and/orthe back surface thereof. Alternatively, the top cryopanel 60 may not beprovided with the adsorbent 74.

The two cryopanel members 62 are disposed on both sides of the secondcooling stage 24 with the cryopump central axis C interposedtherebetween. The cryopanel members 62 are disposed along a planeperpendicular to the cryopump central axis C. For easy understanding,the cryopanel members 62 and the cryopanel mounting member 64 are shownby broken lines in FIG. 2.

The two cryopanel members 62 are disposed at a height position betweenthe upper end and the lower end of the second cooling stage 24 in thedirection of the cryopump central axis C. The two cryopanel members 62are disposed at the same height. The second cooling stage 24 has aflange portion 24 a provided at the end thereof in the directionperpendicular to the cryopump central axis C (the direction of thecentral axis D of the cryocooler 16). The upper end and the lower end ofthe second cooling stage 24 in the direction of the cryopump centralaxis C are defined by the flange portion 24 a. That is, the twocryopanel members 62 are disposed at a height position between the upperend and the lower end of the flange portion 24 a of the second coolingstage 24 in the direction of the cryopump central axis C.

The two cryopanel members 62 are designed as the same components. Thetwo cryopanel members 62 have the same shape and are made of the samematerial. The cryopanel member 62 has a bow shape, a half-moon shape, ora semicircular shape. The cryopanel member 62 is formed of a metalmaterial having a high thermal conductivity, such as copper, forexample, and may be coated with a plating layer such as nickel, forexample.

As shown in FIG. 2, the cryopanel member 62 has an arc portion 78 and achord 79. When viewed in the direction of the cryopump central axis C,the two cryopanel members 62 are disposed symmetrically to each otherwith the intermediate line between them (the central axis D of thecryocooler 16) as the axis of symmetry. The arc portions 78 of the twocryopanel members 62 are on the same circumference centered on thecryopump central axis C. Further, each of the cryopanel members 62 has aline-symmetric shape with a line E passing through the midpoint of thechord 79 (or the cryopump central axis C) and perpendicular to the chord79 as the axis of symmetry.

As shown in FIG. 1, the cryopanel positioning member 67 is fixed to theflange portion 24 a of the second cooling stage 24 and is supported bythe second cooling stage 24. The cryopanel positioning member 67 isformed in an inverted L shape that is turned upside down. By using thecryopanel positioning member 67, the restriction on the length of thecryocooler 16 in the direction of the central axis D is relaxed. Even ifthe flange portion 24 a of the second cooling stage 24 is located offthe cryopump central axis C in the direction of the central axis D ofthe cryocooler 16, by adjusting the length of an upper side portion 67 aof the cryopanel positioning member 67, it is possible to position thesecond-stage cryopanel assembly 20 on the cryopump central axis C. As aresult, an existing cryocooler can be adopted instead of the cryocoolerdesigned exclusively for the cryopump 10. This can help reduce themanufacturing cost of the cryopump 10.

In order to align the second-stage cryopanel assembly 20 with thecryopump central axis C, the upper side portion 67 a of the cryopanelpositioning member 67 may extend from the flange portion 24 a of thesecond cooling stage 24 so as to be separated from the second cylinder25 in the direction of the central axis D of the cryocooler 16, contraryto that shown in FIG. 1. With respect to the cryopump 10 having alarge-diameter intake port 12, the cryopanel positioning member 67having such a shape may be suitable.

The cryopump 10 includes a gas flow adjusting member 50 configured todeflect the flow of the gas flowing in from the shield main opening 34,from the cryocooler structure part 21. The gas flow adjusting member 50is configured to deflect the gas flow, which flows into the mainaccommodation space 65 through the inlet cryopanel 32 or the open area48, from the second cylinder 25. The gas flow adjusting member 50 may bea gas flow deflecting member or a gas flow reflecting member disposedabove and adjacent to the cryocooler structure part 21 or the secondcylinder 25. The gas flow adjusting member 50 is locally provided at thesame position as the shield side portion opening 44 in thecircumferential direction. The gas flow adjusting member 50 has arectangular shape when viewed from above. The gas flow adjusting member50 is, for example, a single flat plate, but may be curved.

The gas flow adjusting member 50 extends from the shield side portion 40and is inserted into the gap region 66. However, the gas flow adjustingmember 50 is not in contact with the top cryopanel 60, the secondcylinder 25, and the other portion having the second cooling temperatureand surrounding the gap region 66. The gas flow adjusting member 50 isthermally coupled to the first cooling stage 22 through the radiationshield 30. Therefore, the gas flow adjusting member 50 is cooled to thefirst cooling temperature.

The cryopump housing 70 is a casing of the cryopump 10, whichaccommodates the first-stage cryopanel 18, the second-stage cryopanelassembly 20, and the cryocooler 16, and is a vacuum container configuredto maintain the vacuum tightness of the internal space 14. The cryopumphousing 70 includes the first-stage cryopanel 18 and the cryocoolerstructure part 21 in a non-contact manner. The cryopump housing 70 ismounted to the room temperature part 26 of the cryocooler 16.

The intake port 12 is defined by a front end of the cryopump housing 70.The cryopump housing 70 has an intake port flange 72 extending radiallyoutward from a front end thereof. The intake port flange 72 is providedover the entire circumference of the cryopump housing 70. The cryopump10 is mounted to a vacuum chamber to be evacuated by using the intakeport flange 72.

The cryopump housing 70 includes a cryopanel accommodation part 76 thatsurrounds the radiation shield 30 in a non-contact with the radiationshield 30, and a cryocooler accommodation part 77 that surrounds thefirst cylinder 23 of the cryocooler 16. The cryopanel accommodation part76 and the cryocooler accommodation part 77 are integrally formed.

The cryopanel accommodation part 76 has a cylindrical or dome shape inwhich the intake port flange 72 is formed at one end and the other endis closed as a housing bottom surface 76 a. Separately from the intakeport 12, an opening through which the cryocooler 16 is inserted isformed in the side wall of the cryopanel accommodation part 76 thatconnects the intake port flange 72 to the housing bottom surface 76 a.The cryocooler accommodation part 77 has a cylindrical shape extendingfrom the opening to the room temperature part 26 of the cryocooler 16.The cryocooler accommodation part 77 connects the cryopanelaccommodation part 76 to the room temperature part 26 of the cryocooler16.

The cryopump 10 includes a water absorbing layer 80 mounted on the outerside of the cryopump housing 70, and a heat insulating layer 82 disposedbetween the cryopump housing 70 and the water absorbing layer 80. Thedew condensation suppressing structure of the cryopump 10 is formed bythe water absorbing layer 80 and the heat insulating layer 82. The dewcondensation suppressing structure includes a water absorbing and heatinsulating sheet 84 having the water absorbing layer 80 on the outerside and having the heat insulating layer 82 on the inner side. Thewater absorbing and heat insulating sheet 84 is configured as a sheet inwhich the water absorbing layer 80 is attached to the outside of theheat insulating layer 82.

The water absorbing and heat insulating sheet 84 covers at least a part,for example, the entire surface, of the outer surface of the cryopumphousing 70. The water absorbing and heat insulating sheet 84 is mountedto both the cryopanel accommodation part 76 and the cryocooleraccommodation part 77 and covers almost the entire surfaces of them. Thewater absorbing and heat insulating sheet 84 is wrapped around the sidesurface of the cryopanel accommodation part 76 and covers the sidesurface. The water absorbing and heat insulating sheet 84 is alsomounted to the housing bottom surface 76 a. The water absorbing and heatinsulating sheet 84 is also wrapped around the cryocooler accommodationpart 77. The water absorbing and heat insulating sheet 84 is mounted tothe cryopump housing 70 by using an appropriate bonding method.

However, the intake port flange 72 is not covered with the waterabsorbing and heat insulating sheet 84. In most cases, even if theintake port flange 72 is exposed, dew condensation does not occur, andtherefore, it is not necessary to mount the water absorbing layer 80and/or the heat insulating layer 82 to the intake port flange 72. In acase of being required, the water absorbing layer 80 and/or the heatinsulating layer 82 may be mounted to the intake port flange 72.

The water absorbing layer 80 is formed of a material having an excellentwater absorption property compared to a structural material (forexample, stainless steel such as SUS304) forming the outer surface ofthe cryopump housing 70 and/or compared to a heat insulating materialforming the heat insulating layer 82. The water absorbing layer 80 isformed of, for example, a water absorbing material such as awater-absorbent resin or a water-absorbent porous material, whichchemically and/or physically adsorbs water, or a material containingsuch a water absorbing material. For the water absorbing layer 80,products commercially available as general names such as awater-absorbent resin, a water absorbing polymer, and water absorbingsheet can be appropriately adopted. Alternatively, the water absorbinglayer 80 may be formed of a material such as felt or sponge that retainswater at least temporarily.

The heat insulating layer 82 is formed of a material having a smallerthermal conductivity than the structural material forming the outersurface of the cryopump housing 70. The heat insulating layer 82 may beformed of various known heat insulating materials such as a foam-basedheat insulating material and/or a fiber-based heat insulating material.

A thickness 86 of the heat insulating layer 82 is determined such thatthe temperature of the water absorbing layer 80 is maintained at atemperature higher than 0° C. during the regeneration of the cryopump10. The thickness 86 of the heat insulating layer 82 may be determinedsuch that the temperature of the water absorbing layer 80 is maintainedat a temperature higher than 5° C. or higher than 10° C. In other words,the thickness 86 of the heat insulating layer 82 is determined such thatthe temperature of the outer surface of the heat insulating layer 82does not fall below the freezing point of water during the regenerationof the cryopump 10.

The operation of the cryopump 10 having the above configuration will bedescribed below. When the cryopump 10 is operated, first, the interiorof the vacuum chamber is roughed to about 1 Pa with another appropriateroughing pump before the operation. Thereafter, the cryopump 10 isoperated. The first cooling stage 22 and the second cooling stage 24 arerespectively cooled to the first cooling temperature and the secondcooling temperature by the driving of the cryocooler 16. Accordingly,the first-stage cryopanel 18 and the second-stage cryopanel assembly 20thermally coupled to these are also respectively cooled to the firstcooling temperature and the second cooling temperature.

The inlet cryopanel 32 cools the gas which comes flying from the vacuumchamber toward the cryopump 10. A gas having a sufficiently low vaporpressure (for example, 10⁻⁸ Pa or less) at the first cooling temperaturecondenses on the surface of the inlet cryopanel 32. This gas may bereferred to as a first type gas (also called a type 1 gas). The type 1gas is, for example, water vapor. In this way, the inlet cryopanel 32can exhaust the type 1 gas. A part of a gas in which vapor pressure isnot sufficiently low at the first cooling temperature passes through theinlet cryopanel 32 or the open area 48 and enters the main accommodationspace 65. Alternatively, the other part of the gas is reflected by theinlet cryopanel 32 and does not enter the main accommodation space 65.

The gas that has entered the main accommodation space 65 is cooled bythe second-stage cryopanel assembly 20. A gas having a sufficiently lowvapor pressure (for example, 10⁻⁸ Pa or less) at the second coolingtemperature condenses on the surface of the second-stage cryopanelassembly 20. This gas may be referred to as a second type gas (alsocalled a type 2 gas). The type 2 gas is, for example, nitrogen or argon.In this way, the second-stage cryopanel assembly 20 can exhaust the type2 gas. A condensation layer for the type 2 gas can grow largely on thefront surface of the top cryopanel 60 because it directly faces the mainaccommodation space 65. The type 2 gas is a gas that does not condenseat the first cooling temperature.

A gas in which vapor pressure is not sufficiently low at the secondcooling temperature is adsorbed by the adsorbent 74 of the second-stagecryopanel assembly 20. This gas may be referred to as a third type gas(also called a type 3 gas). The type 3 gas is, for example, hydrogen. Inthis way, the second-stage cryopanel assembly 20 can exhaust the type 3gas. Therefore, the cryopump 10 can exhaust various gases bycondensation or adsorption and can make the degree of vacuum of thevacuum chamber reach a desired level.

An exhaust operation is continued, whereby gas is accumulated in thecryopump 10. In order to discharge the accumulated gas to the outsidethe regeneration of the cryopump 10 is performed. If the regeneration iscompleted, the exhaust operation can be started again.

In order to promote the temperature rise of the cryopump 10 and shortenthe regeneration time, a purge gas is generally introduced into thecryopump housing 70 at the start of the regeneration. Due to there-vaporization of the purge gas or the accumulated gas, the interior ofthe cryopump housing 70 is filled with gas, and therefore, a vacuumadiabatic effect is lost unlike during the exhaust operation. Heatexchange between the cryopanel and the cryopump housing 70 is promotedthrough the gas. Immediately after the start of the reproduction, thecryopanel is still cooled to a cryogenic temperature, so that thecryopump housing 70 can be cooled.

Further, since the cryopump 10 has the large main accommodation space65, it is possible to store a large amount of the type 2 gas. At therelatively early stage of the regeneration, the type 2 gas dissolvesinto a liquid. As described above, since the type 2 gas is nitrogen,argon, or the like, the liquefied gas is very cold. The liquefied gasmay flow down to the bottom portion of the radiation shield 30 or thecryopump housing 70 and come into contact with the inner surface of thecryopump housing 70. Then, the cryopump housing 70 is significantlycooled. For this reason, moisture in the ambient air may condense orfrost may adhere to the outer surface of the cryopump housing 70. Duringthe regeneration, the cryopump 10 is gradually heated to roomtemperature, so that the frost will eventually melt. If there is a lotof frost attached, it melts into a lot of water that can drop. It mayresult in wetting other equipment or items around the cryopump 10 or thefloor surface.

The cryopump 10 according to the embodiment includes the water absorbinglayer 80 mounted on the outer side of the cryopump housing 70. Moisturethat tends to adhere to the outer surface of the cryopump housing 70 isabsorbed by the water absorbing layer 80. Therefore, dew condensation onthe cryopump 10 can be suppressed. Since the dew condensation issuppressed, the dropping of water to the surroundings of the cryopump 10or the floor surface is also suppressed.

Further, the heat insulating layer 82 is disposed between the cryopumphousing 70 and the water absorbing layer 80. The temperature decrease ofthe outer surface of the heat insulating layer 82 is smaller than thetemperature decrease of the cryopump housing 70. The temperaturedifference between the outside air temperature and the water absorbinglayer 80 can be made smaller than in a case where the water absorbinglayer 80 is directly mounted to the cryopump housing 70 without the heatinsulating layer 82. Therefore, dew condensation on the cryopump 10 canbe suppressed.

If the temperature of the outer surface of the heat insulating layer 82is lower than room temperature, dew condensation may occur. In order toprevent the dew condensation only by the heat insulating layer 82without providing the water absorbing layer 80, the thickness 86 of theheat insulating layer 82 has to be sufficiently thick. In this case, therequired thickness 86 of the heat insulating layer 82 may be so largethat it is difficult to actually mount it on the cryopump housing 70.

However, since the cryopump 10 according to the embodiment has the waterabsorbing layer 80, it is possible to absorb the moisture that maycondense on the outer surface of the heat insulating layer 82. The outersurface of the heat insulating layer 82 may be cooled to a certaindegree from room temperature, and thus it is possible to make the heatinsulating layer 82 thin. It is expected that the water absorbing layer80 itself does not need that much thickness. Therefore, by combining thewater absorbing layer 80 and the heat insulating layer 82, a dewcondensation suppressing structure having a small thickness as a wholecan be realized, and the mounting on the cryopump 10 becomes easier.

In a typical cryopump of the related art, an electric heater such as aband heater is wound around a housing in order to suppress dewcondensation. The cryopump 10 according to the embodiment also has anadvantage that such an electric heater is not required (therefore, thecryopump 10 according to the embodiment does not have an electric heaterfor heating the cryopump housing 70).

Further, the cryopump 10 according to the embodiment does not require awater receiving tray also called a drain pan.

The cryopump 10 includes the water absorbing and heat insulating sheet84 having the water absorbing layer 80 on the outer side and having theheat insulating layer 82 on the inner side. In a case where the waterabsorbing layer 80 and the heat insulating layer 82 are separate layers,a two-step operation is required in which the heat insulating layer 82is first mounted to the cryopump housing 70 and the water absorbinglayer 80 is then mounted to the heat insulating layer 82. In the case ofthe water absorbing and heat insulating sheet 84, the water absorbinglayer 80 and the heat insulating layer 82 can be mounted together to thecryopump housing 70, and therefore, manufacturing becomes easier.

In a case where the temperature of the outer surface of the waterabsorbing layer 80 is lower than 0° C., the condensed water may befrozen on the outer surface of the water absorbing layer 80. The icelayer is separated from the water absorbing layer 80 and adheres ontothe water absorbing layer 80. When the ice layer melts due to thetemperature rise of the cryopump 10, water may drop. However, accordingto the embodiment, the thickness 86 of the heat insulating layer 82 isdetermined such that the temperature of the water absorbing layer 80 ismaintained at a temperature higher than 0° C. during the regeneration ofthe cryopump 10. Therefore, the formation of the ice layer on the waterabsorbing layer 80 is suppressed, and the dropping of water is alsosuppressed.

The present invention has been described above based on the examples. Itwill be understood by those skilled in the art that the presentinvention is not limited to the embodiments described above, variousdesign changes can be made, various modification examples can be made,and such modification examples are also within the scope of the presentinvention.

In the embodiment described above, the water absorbing and heatinsulating sheet 84 is mounted to both the cryopanel accommodation part76 and the cryocooler accommodation part 77. However, this is notessential. The water absorbing layer 80, the heat insulating layer 82,and/or the water absorbing and heat insulating sheet 84 may be mountedto only one of the cryopanel accommodation part 76 and the cryocooleraccommodation part 77.

The water absorbing layer 80, the heat insulating layer 82, and/or thewater absorbing and heat insulating sheet 84 may be mounted to thecryopump housing 70 so as to cover only a part of the outer surface ofthe cryopump housing 70. For example, the water absorbing and heatinsulating sheet 84 may be mounted only to the lower portion of thecryopanel accommodation part 76. With this configuration, the dewcondensation water flowing down from the upper portion of the cryopanelaccommodation part 76 can be absorbed by the water absorbing and heatinsulating sheet 84, and thus the dropping of the dew condensation watercan be suppressed. Further, there is a case where the cryocooleraccommodation part 77 is provided with a constituent element such as avalve or a sensor, which protrudes outward from the tubular portion.Such a constituent element may not be covered by the water absorbing andheat insulating sheet 84.

The water absorbing layer 80 may be disposed between the cryopumphousing 70 and the heat insulating layer 82. That is, the waterabsorbing layer 80 may be disposed inside the heat insulating layer 82.For example, as shown in FIG. 3, the cryopump housing 70 can havecorners or curved portions. The thickness 86 of the heat insulatinglayer 82 is relatively large in order to provide good thermalinsulation. For this reason, a case where the heat insulating layer 82is unlikely to come into close contact with the corners or the curvedportions and is difficult to completely cover them is also assumed. Insuch a case, as shown in the drawing, the corner or the curved portionof the cryopump housing 70 may be covered with the water absorbing layer80.

Further, as shown in FIG. 4, in a case where it is difficult for theheat insulating layer 82 to completely cover the corners or the curvedportions of the cryopump housing 70, the water absorbing layer 80 maycover the heat insulating layer 82 from the outside. In this case, sincethe heat insulating layer 82 is not provided at the corner or the curvedportion of the cryopump housing 70, a gap 87 may be formed between thecorner or the curved portion and the water absorbing layer 80.

As shown in FIG. 5, the cryopump 10 may include a drain pan 88. Thedrain pan 88 is provided as a water receiving tray disposed below thecryopump housing 70, and is configured to prevent the dew condensationwater from dripping on a floor surface 94 and/or to receive and storethe dropping dew condensation water. The drain pan 88 is mounted to thecryopanel accommodation part 76 of the cryopump housing 70. The drainpan 88 may be fastened together with a caster 90 to the cryopanelaccommodation part 76. A heat insulating spacer 92 may be insertedbetween the drain pan 88 and the cryopanel accommodation part 76. Thedrain pan 88 may be mounted to the cryopump housing 70 by another methodsuch as being suspended from the intake port flange 72.

The water absorbing layer 80, the heat insulating layer 82, and/or thewater absorbing and heat insulating sheet 84 is mounted to thecryocooler accommodation part 77. The water absorbing layer 80, the heatinsulating layer 82, and/or the water absorbing and heat insulatingsheet 84 may be mounted to the cryopanel accommodation part 76. In thisway, the drain pan 88 may be used together with the dew condensationsuppressing structure according to the embodiment.

In the above description, the horizontal cryopump has been exemplified.However, the present invention is also applicable to other verticalcryopumps. The vertical cryopump refers to a cryopump in which thecryocooler 16 is disposed along the cryopump central axis C of thecryopump 10. In that case, the cryocooler accommodation part 77 isinstalled not on the side surface of the cryopanel accommodation part 76but on the housing bottom surface 76 a. Further, the internalconfiguration of the cryopump, such as the arrangement, the shape, thenumber, or the like of a cryopanel, is not limited to the specificembodiment described above. Various known configurations can beappropriately adopted.

The present invention can be used in the field of a cryopump.

It should be understood that the invention is not limited to theabove-described embodiment, but may be modified into various forms onthe basis of the spirit of the invention. Additionally, themodifications are included in the scope of the invention.

What is claimed is:
 1. A cryopump comprising: a cryopump housing; and a water absorbing layer mounted on an outer side of the cryopump housing.
 2. The cryopump according to claim 1, further comprising: a heat insulating layer disposed between the cryopump housing and the water absorbing layer.
 3. The cryopump according to claim 2, further comprising: a water absorbing and heat insulating sheet having the water absorbing layer on an outer side thereof and having the heat insulating layer on an inner side thereof.
 4. The cryopump according to claim 2, wherein a thickness of the heat insulating layer is determined such that a temperature of the water absorbing layer is maintained at a temperature higher than 0° C. during regeneration of the cryopump. 